Polyamide, from condensed cyclic dicarboxylic acid and branched chain diamine

ABSTRACT

Polyamides formed from 80 to 100 mol %, relative to the polyamide, of at least one structural element of the formula I ##STR1## and 20 and 0 mol % of at least one structural element of the formulae II and/or IIa ##STR2## wherein R 1  and R 2  are lower alkyl, or together are alkylene, R 3  is naphthylene or anthracenylene or the corresponding cycloaliphatic ring systems, R 4  is alkylene, R 5  is alkylene or an aromatic radical, and R 6  is alkylene, cycloalkylene or a divalent araliphatic radical. The polyamides have melting points which render possible processing by thermoplastic shaping processes.

The present invention relates to thermoplastic crystalline polyamides formed from condensed cyclic dicarboxylic acids, 1,10-diaminodecanes substituted by secondary alkyl in the 1,10-position, and optionally aminocarboxylic acids, other dicarboxylic acids and diamines, to a process for producing these polyamides, and to their use as moulding compounds in thermoplastic shaping processes.

Crystalline polyamides formed from terephthalic acid and 1,10-diaminodecanes substituted by secondary alkyl in the 1,10-position are described in the European Patent Application No. B1-0001786. Some of these polyamides have melting points so high that they cannot be processed by shaping processes customarily used for thermoplastics.

The present invention thus relates to a polyamide formed from aromatic dicarboxylic acids, diamines and optionally aminocarboxylic acids and having a reduced solution viscosity of at least 0.3 dl/g, measured on a 0.5% solution in m-cresol at 25° C., which polyamide consists of 80 to 100 mol %, relative to the polyamide, of at least one recurring structural element of the formula I ##STR3## and 20 to 0 mol % of at least one recurring structural element of the formulae II and/or IIa ##STR4## wherein R¹ is alkyl having 1 to 4 C atoms, and R² is alkyl having 1 to 8 C atoms, or R¹ and R² together are tri-, tetra- or pentamethylene, R³ is a radical of the formulae ##STR5## the six-membered rings being aliphatic or aromatic hydrocarbon radicals, R⁴ is alkylene having 5 to 11 C atoms, R⁵ is an aliphatic radical having 2 to 12 C atoms, or an aromatic hydrocarbon radical having 6 to 12 C atoms, and R⁶ is straight-chain alkylene having 2 to 12 C atoms, or a cycloaliphatic or araliphatic radical.

The reduced solution viscosity is preferably 0.3 to 2.5, and particularly 0.4 to 1.5. The polyamide preferably contains 0 to 10 mol % of structural elements of the formulae II and/or IIa, and in particular the polyamide is a homopolyamide having 100 mol % of structural elements of the formula I.

R¹ and R² can be straight-chain or branched-chain alkyl. Preferably, however, R¹ and R² are straight-chain alkyl. In a preferred embodiment, R¹ and R² are C₁ -C₄ -alkyl and especially C₁ -C₂ -alkyl. Examples of alkyl are: methyl, ethyl, n-propyl, i-propyl, n-butyl, sec-butyl, n-pentyl, n-hexyl, n-heptyl and n-octyl. R¹ and R² together as alkylene are preferably trimethylene, particularly tetramethylene, and more particularly pentamethylene.

R³ can for example correspond to the following formulae: ##STR6##

R³ is preferably 9,10-anthracenylene, 1,5-naphthylene and in particular 1,4-naphthylene.

When R⁵ is an aliphatic radical, it is especially straight-chain alkylene having 2-12 C atoms, and preferably straight-chain alkylene having 4-10C atoms; alkylene groups R⁶ preferably contain 2-10 C atoms.

Aromatic hydrocarbon radicals denoted by R⁵ can be unsubstituted or substituted, for example by alkyl groups having 1-4 C atoms. They are for example monocyclic, condensed polycyclic or uncondensed bicyclic aromatic radicals; and in the case of the last-mentioned the aromatic hydrocarbon nuclei can also be bound together by way of a bridge-member, such as --O--, --S--, --CH₂ -- or --SO₂ --. In particular, R⁵ is a 4,4'-biphenylene, 4,4'-diphenyl ether or 4,4'-diphenylsulfone radical, and especially the 1,3-phenylene group and more especially the 1,4-phenylene group.

As a cycloaliphatic radical, R⁶ is for example the 1,3-cyclopentylene group, the 1,3- or 1,4-cyclohexylene group or the 4,4'-dicyclohexylmethane group, whilst as an araliphatic radical, R⁶ is in particular 1,3-xylylene.

R⁴ as alkylene is preferably straight-chain, and can be for example: 1,5-pentylene, 1,6-hexylene, 1,7-heptylene, 1,8-octylene, 1,9-nonylene, 1,10-decylene and 1,11-undecylene.

Preferred polyamides are those having recurring structural elements of the formula I wherein R¹ and R² are methyl or ethyl, or R¹ and R² together are tetra- or pentamethylene.

In a particularly preferred embodiment, the polyamide is one having recurring structural elements of the formula ##STR7## wherein R¹ is methyl, R² is methyl or ethyl, or R¹ and R² together are tri- or tetramethylene.

More especially preferred polyamides are those having recurring structural elements of the formula Ia wherein R¹ and R² together are pentamethylene.

Further subject matter of the present invention is a process for producing polyamides, which process comprises polycondensing 40 to 50 mol % of a dicarboxylic acid of the formula III

    HOOC--R.sup.3 --COOH                                       (III)

and 10 to 0 mol % of an aminocarboxylic acid of the formula IV or of a dicarboxylic acid of the formula V

    HOOC--R.sup.4 --NH.sub.2                                   (IV)

    HOOC--R.sup.5 --COOH                                       (V),

or of the polyamide-forming derivatives thereof, with 40 to 50 mol % of a diamine of the formula VI ##STR8## and 10 to 0 mol % of a diamine of the formula VII

    H.sub.2 N--R.sup.6 --NH.sub.2                              (VII),

the mol % values being relative to the polyamide.

The compounds of the formulae III, IV, V and VII are known, and some are available commercially. The diamines of the formula III are described in the European Patent Application No. B1-0001786.

Amide-forming derivatives are for example dihalides, particularly dichlorides, dialkyl esters having preferably 1 to 4 C atoms in the alkyl, diphenyl esters, lactams and dinitriles.

The polyamides of the invention are produced by customary methods in equipment normally used for the purpose. The usual methods are for example: melt condensation, polycondensation in solution, interfacial polycondensation and solid-phase polycondensation, and combinations of such methods.

The preferred method of production is the melt polycondensation process, which in general is carried out in 3 stages. There are firstly formed salts from essentially stoichiometric amounts of dicarboxylic acid and a diamine in a suitable solvent.

Suitable inert organic solvents are for example: cycloaliphatic alcohols, such as cyclopentanol and cyclohexanol, and particularly aliphatic alcohols having up to 6 C atoms, such as methanol, ethanol, n-propanol, butanols, pentanols and hexanols, as well as mixtures of such solvents with water.

Precondensation of the salt in the melt is subsequently performed at temperatures of about 220° to 320° C. The precondensate is then polycondensed in the melt, advantageously under an inert gas and at normal pressure or in vacuo, at about 220° to 320° C.

To obtain higher molecular weights, solid, partially-crystalline precondensates can be polycondensed in the solid phase, advantageously in vacuo and/or inert gas, and at temperatures which are about 20° C. below the melting point of the polycondensate.

The polycondensation in solution is advantageously performed with the use of dicarboxylic acid dichlorides and diamines, optionally with the addition of an HCl-acceptor.

The polyamides according to the invention are partially crystalline and are distinguished by good stability to hydrolysis, dimensional stability and low moisture absorption. Compared with the polyamides formed from terephthalic acid and diamines of the formula VI, the polyamides according to the invention have surprisingly lowered melting points, by virtue of which even the thermoplastic processibility of the inventive polyamides is rendered possible.

The polyamides according to the invention can therefore be used as moulding compounds in shaping processes for thermoplastics, for example injection moulding and extrusion, for producing moulded articles. It is also possible to produce fibers and filaments by the melt-spinning process.

The present invention hence relates also to the use of these polyamides in any one of these processes.

The following Examples further illustrate the present invention. DSC is an abbreviation for Differential-Scanning-Calorimetry.

EXAMPLE 1

In a flask provided with stirrer, dropping funnel and reflux condenser, 4.322 g of naphthalene-1,4-dicarboxylic acid in a mixture of 40 ml of water and 120 ml of ethanol are heated to reflux temperatures, and 5.132 g of 3,12-diamino-2,13-dimethyltetradecane are introduced dropwise, and the dropping funnel is rinsed out with 20 ml of ethanol. After being refluxed for 4 hours, the reaction mixture is cooled, and the formed salt is filtered off. The yield after drying in vacuo at 80° C. is 8.9 g of salt (94% of theory). 5 g of this salt are sealed under nitrogen in a bomb tube, and heated in a salt bath at 270° C. for 2 hours, in the course of which there is formed a clear melt which, on cooling, solidifies to form an opaque substance. The precondensate is removed from the bomb tube, and is subsequently heated in a condensing tube, as nitrogen is being passed through, at 280° C. for 5 hours. On cooling, the melt crystallises into the form of an opaque material.

The reduced solution viscosity, measured on a 0.5% solution in m-cresol at 25° C., is 0.45 dl/g.

In the DSC, the polyamide shows a melting peak having a maximum at 239° C.

EXAMPLE 2

In a polycondensation apparatus, through which nitrogen is being passed, a mixture of 1.9859 g of naphthalene-1,4-dicarboxylic acid diphenyl ester and 1.5337 g of 4,13-diamino-3,14-dimethylhexadecane is heated, in the course of one hour, from 220° to 280° C. There is then applied a vacuum of about 0.1 mbar, and the temperature is held for a further hour at 280° C. in order to hasten the polycondensation and to completely distil off the phenol being released in the process. On cooling, the melt crystallises to form an opaque substance;

melting point (DSC): 243° C.;

reduced solution viscosity: 0.39 dl/g.

EXAMPLE 3

By a procedure analogous to that of Example 2, a mixture of 1.7495 g of naphthalene-1,4-dicarboxylic acid diphenyl ester and 1.6114 g of 1,10-diamino-1,10-dicyclohexyldecane is polycondensed to a polyamide;

melting point (DSC): 251° C.;

reduced solution viscosity: 0.55 dl/g.

EXAMPLE 4

In a manner corresponding to that of Example 2, 2.02 g of 4.13-diamino-3,14-diethylhexadecane are polycondensed with 2.37 g of naphthalene-1,4-dicarboxylic acid diphenyl ester to a polyamide;

melting point (DSC): 258° C.;

reduced solution viscosity: 0.44 dl/g. 

What is claimed is:
 1. A polyamide, formed from at least one dicarboxylic acid and diamine, having a reduced solution viscosity of at least 0.3 dl/g, measured on a 0.5% solution in m-cresol at 25° C., and having 100 mol %, relative to the polyamide, of recurring structural elements of formula I ##STR9## wherein R¹ is alkyl having 1 to 4 C atoms, and R² is alkyl having 1 to 8 C atoms, or R¹ and R² together are tri-, tetra- or pentamethylene, R³ is a radical of the formulae ##STR10## the six-membered rings being aliphatic or aromatic hydrocarbon radicals.
 2. A polyamide according to claim 1, wherein R¹ and R² are methyl or ethyl, or R¹ and R² together are tetra- or pentamethylene.
 3. A polyamide according to claim 1, wherein R³ is a radical of the formula ##STR11##
 4. A polyamide according to claim 1, which consists of structural elements of the formula ##STR12## wherein R¹ is methyl and R² is methyl or ethyl, or R¹ and R² together are tri- or tetramethylene.
 5. A polyamide according to claim 1 which consists of structural elements of formula ##STR13## wherein R¹ and R² together are pentamethylene.
 6. A molded article, fiber or filament of the polyamide according to claim
 1. 